1 Field of the Invention
The present invention relates generally to the field of fluorescence spectroscopy. More particularly, the present invention relates to a low cost portable fiber optic fluorometer that is packaged as a personal computer peripheral or on a personal computer expansion card and is based on interchangeable modules.
2. Discussion of the Related Art
Historically, fluorescence spectroscopy has been widely used in chemical, biochemical, and biomedical research. Although there are a virtually unlimited number of different ways in which fluorescence spectroscopy could be applied, specific fluorescence spectroscopy applications include chemical sensors, process control systems, systems for studying cellular phenomena, systems for determining molecular structure, and temperature and viscosity measurement systems.
A number of different fluorescence spectroscopy techniques exist, including intensity-based techniques and fluorescence lifetime techniques. According to intensity-based techniques, information regarding a system under study is obtained by measuring the relative intensity of emissions from a sample at one or more wavelengths. According to fluorescence lifetime techniques, information is obtained by exciting a fluorescent sample with an excitation signal in the form of a pulse of light, and then directly measuring the exponential decay of the resulting emission signal from the sample. A variation of the fluorescence lifetime technique is phase fluorometry. According to phase fluorometry, information is obtained by illuminating a fluorescent sample with a modulated excitation signal, thereby causing the sample to emit an emission signal which is also modulated. The time delay between excitation of the sample and emission causes a phase difference between the excitation and emission signals. The phase difference is a function of the fluorescence lifetime; accordingly, measuring the phase difference enables the fluorescence lifetime of the system under study to be calculated. Thus, in contrast to the fluorescence lifetime techniques which measure a fluorescence lifetime directly, phase fluorometry involves measuring a fluorescence lifetime indirectly by measuring the phase difference between an excitation signal and an emission signal.
The main advantage of fluorescence spectroscopy is the high sensitivity which can be achieved due to the favorable time scale of fluorescence emissions. Nevertheless, despite this advantage, fluorescence spectroscopy has failed to achieve widespread commercial acceptance outside the laboratory research setting.
The lack of widespread commercial acceptance is due to the fact that existing fluorometers are bulky, expensive, require precise optical alignment, and are difficult to calibrate. Specifically, existing fluorometers comprise numerous large and expensive components. The excitation source is typically a laboratory grade light source, such as a gas laser or a high-powered arc lamp. The detector is typically a spectrograph which collects and records the entire spectrum of light returned from the system under study. (Existing fluorometers are designed to permit the study of fluorescence emission at a wide range of wavelengths, e.g., from the ultraviolet to the near infrared.) Moreover, because precise optical alignment is required between the various subcomponents, existing fluorometers require an optical bench which floats on a pneumatic system in order to reduce vibrations. Finally, calibration of existing fluorometers is extremely difficult, especially in a commercial setting where environmental conditions are more likely to be adverse as compared to a laboratory setting. Existing fluorometers are thus not only expensive to purchase but also are expensive to set up and maintain.
Thus, what is needed is a fluorometer that is relatively inexpensive, that is small in size, that is tolerant to environmental hazards such as vibration, and/or that is relatively easy to calibrate.